How do enzyme inhibitors affect enzymes?

You have to look at the word "inhibit". Inhibit means to prevent or hold back an action. If enzymes are biological catalysts, which work to speed up reactions at relatively low temperatures, then something that would inhibit an enzyme would decrease reaction rate. Enzyme inhibitors work by preventing the substrate (like a polypeptide) from attaching to the active site (where the reaction occurs on the enzyme).

There are competitive inhibitors and non-competitive inhibitors. Competitive inhibitors prevent the substrate from binding to the active site by simply "getting in the way". They lodge in the active site (don't necessarily have to fit perfectly) and bounce the substrate right back. Non-competitive inhibitors are not involved with the active site. They bind somewhere on the enzyme and cause the enzyme to change shape. Enzymes are very selective when choosing which substrates it will accept. This, among other factors, ensures the diversity of enzymes. Much like denaturation, the change in shape caused by the non-competitive inhibitor causes the active site to not be a perfect match for the substrate. Even if the R-groups on the enzyme line up with the positive/negative charges of the substrate, geometrically it won't work.